Fillet weld inspection system

ABSTRACT

A device for underwater detection of flaws in welds, especially lap welds as distinguished from butt welds wherein a filleted weld is made, said device embodying ultrasonic transducers arranged to emit and receive a sonic beam at angles such as to pass through the weld at an angle corresponding substantially to the inclination of the weld and to be adjustable for welds of different inclination and for beam travel through different configurations of weldments.

BACKGROUND OF THE INVENTION

In underwater repair operations, fillet welds are used extensively dueto the relative ease of installing of a fillet weld as opposed toinstalling a butt weld. A butt weld takes more skill on the part of thewelder and is more susceptible to defects due to the varying influencesencountered in the underwater environment. For example, if a crack isfound in an underwater structure such as the hull of a ship, it isgenerally preferred to weld a "doubler" or additional plate over thecracked area using a fillet weld than it is to cut out the hull platearound the defective area and install a sound piece of plate in itsplace. Although the butt weld will give a smoother contour to the hull,the ship must be dry-docked during the operation or else a watertighthabitat must be built around the defective area. Moreover, the defectivematerial that is cut out must be discarded without damaging the habitatand a new piece of plate must be cut to size to exactly fit the holewhere the damaged plate was removed and the diver must have access intoand out of the habitat without disturbing the watertight environment.The new plate must be carefully held in alignment during the initialstages of welding and the welder has to weld into an "open groove" withpoor edge preparation and no backing. Any water, oil, grease or otherbilge on the interior of the ship must be drained and cleaned to barethe metal in the welding area.

In constrast, a double plate type of repair may be performed in the wet,that is, underwater, with minimum cleaning and edge preparation, isuncomplicated and requires only minor skill on the part of the welder.Thus, fillet welding doubler plates is eminently more practical in termsof expense, time and quality of the end result and so is used in almostall repair operations performed underwater.

Devices for ultrasonic inspection have been used extensively on landand, to some extent, underwater in determining the quality of buttwelds; however, ultrasonic inspection of "fillet" or "lap" welds has notbeen effectively developed. The reason for this is the inherent geometryof the lap joint which does not lend itself to the current methods ofstraight beam or shear wave inspection, and fillet welds generally areused on less critical joints where inspection has not been required.Recently, however, because of more stringent quality control of repairoperations, the need for a device for providing for better inspection offillet welds has risen, since that used for butt welds is not suitable.It is the purpose of this invention to provide inspection means designedparticularly to enable accurate determination of the conditions offillet welds, including such defects as lack of penetration, lack offusion, slag inclusions, porosity, cracks, intergranular cracking of theweld and base metal, corrosion, stress corrosion cracks, inclusions andother defects.

SUMMARY OF THE INVENTION

The device as herein illustrated is for detecting flaws in a fillet weldjoining two parts in overlapping relation and comprises a firsttransducer, a support for supporting said first transducer at one sideof the parts at an angle such that the beam emitted therefrom travelsfrom the one side to the other of the overlapping parts and is reflectedby the part at the other side back to the support at the one side, andat a point therealong spaced from the first transducer such that duringthe course of its travel, the beam pass through the weld along a pathsubstantially parallel to the inclined surface of the weld and meansmounting a second transducer on the support at said point at an angle toreceive said reflected beam. A carriage block is mounted on the supportfor movement relative to one end of the support, and means are providedfor fixing the carriage block in a predetermined adjusted position. Thesupport and carriage block contain longitudinally aligned openings fromtop to bottom in which the transducers are adjustably fixed atconverging angles, e.g., of approximately 18 degrees from the verticalwhen the inspection is done using water as the couplant.

The invention will now be described in greater detail with reference tothe accompanying drawings, wherein:

FIG. 1 diagrammatically illustrates the device for detectingimperfections in a lap or filleted joint;

FIG. 2 is a perspective of the device;

FIG. 3 is an elevation of a cathode ray screen wherein the peak at theleft-hand side represents the sound at the entry point and the peak atthe right-hand side the sound received and wherein the distance betweenpeaks represents the total distance of the sound path through the mediaand the height of the right-hand peak represents the amount or qualityof the sound received by the receiving transducer;

FIG. 4 is similar to FIG. 3 showing the peak at the right-hand side ofthe screen much lower than the peak at the left-hand side, thusindicating poor sound reception and thus the presence of a defect;

FIG. 5 shows the peak at the left-hand side with no peak at theright-hand side, indicating a major defect which has dissipated the beamentirely or that the device has been moved beyond the area of the weld;and

FIG. 6 is an ultrasonic generator provided with a cathode ray screen onwhich the signals are depicted.

Referring now to the drawings, FIGS. 1 and 2, one embodiment of theinvention is disclosed, wherein the device comprises a support 10mounting two transducers 12 and 14 in longitudinally spaced relation atconverging angles such that, in use, when the device is moved across andalong the fillet at one side, the beam emitted from one transducer willenter the part at the one side, pass through the fillet along a pathsubstantially parallel to the inclined surface thereof and through theother part at the other side, be reflected in said part at the otherside and transmitted therethrough at an angle to be received by theother transducer.

The support 10 as illustrated herein comprises an elongate, rigid block16 of rectangular cross section at one end of which there is anextension 18 of a narrower front-to-back width, the rear side of whichis a continuation of the rear side of the block 16 and the front side 20of which is situated rearwardly of the front side 22 of the block 20 andparallel thereto. The front side 20 of the extension has aforwardly-projecting, longitudinally-extending tongue 26 parallel to theupper and lower sides of the block and its extension and longitudinallyof the tongue, there is an elongate slot 28 which extends through theextension from the front side of the tongue to the back side of theextension. The front side 20 of the extension and the end 30 of theblock from which it extends define a recess 32 and a carriage block 34is mounted in the recess on the tongue for sliding movement along theextension relative to the end 30 of the block. The carriage block 34corresponds substantially in front-to-back width to the depth of therecess 32 and is provided at its rear side with a groove 35 for slidablyengaging the tongue so that it is guided rectilinearly in its movementrelative to the block 16. The carriage block is adjustably secured tothe extension by a bolt 36 provided with a head 38 at one end which ismounted in the slot 28 with its shank extending forwardly through a hole40 in the block and has on its forwardly-projecting end a nut 42.

The supporting block 16 and carriage block 34 contain longitudinallyaligned openings 44 and 46 which extend from the top to the bottom forreceiving the transducers 12 and 14. Set screws 48 - 48' and 50 - 50'provide for fixing the transducers 12 and 14 in the openings and foradjusting them therein to provide the proper inclination of thetransducers relative to each other. The openings 44 and 46 are inclinedat corresponding angles of approximately 18 degrees to the vertical whenthe coupling medium which is used to transmit the sound between thetransducer and the article to be inspected is water, the article to beinspected is steel, and the desired angle of transmission of the soundthrough the article to be inspected is 45 degrees. This angle may beadjusted for other conditions in accordance with the indices ofrefraction of the coupling medium and the material to be inspected, aswill be apparent to those skilled in the art.

The transducer 12 emits an ultrasonic beam and, as disclosed in FIG. 1,is arranged so that when the device is placed in parallel relation tothe lap joint to be tested with its bottom planar surface 52 resting ona plate 53, for example, which has been lap-welded to a plate 54 bymeans of a fillet weld 56, a beam a emitted from the transducer 12 willenter the plate 53 at the point A, pass through the weld 56 atapproximately 45°, and from thence through the plate 54 to the point B,whereupon it will be reflected through an angle of approximately 90° soas to recross the plate 54, leave the plate 54 at the point C and enterthe transducer 14. If the weld is sound, the beam a transmitted throughit will be substantially unimpeded so that a strong signal substantiallyas strong as that emitted from the transducer 12 will be received by thetransducer 14, indicating the absence of defects. Such a signal isrepresented by the peak marked II in FIG. 3 of the drawings which isnearly as high as the peak marked I which represents the strength of thesignal emitted from the transducer 12. The presence of a defect, ofcourse, will result in dispersion of the beam to a certain extent and,depending upon the attenuating qualities of the defect, will result in adiminution of the signal as represented, for example, in FIG. 4. Aserious defect will normally result in complete dispersion of the signalas represented in FIG. 6 or will indicate that the device has been movedbeyond the area of the weld.

The signals transmitted and received by the transducers are graphicallydisplayed e.g., on a cathode ray screen 58 such as is shown in FIGS. 3,4 and 5 which has along the vertical edge a scale 62 representing thestrength of the signal. The distance between the peaks I and IIrepresents the total distance of the sound travel through the media. Theheight of the first peak I is a constant in that it simply indicates thestrength of the signal produced by the first transducer. The height ofthe second peak II is directly proportional to the amount of the signalreceived by the second transducer.

The adjustment of the carriage block 34 along the extension and, hence,of the transducers relative to each other provide for use of the devicewith lap welds and base materials of different thickness. For aparticular article to be inspected, having known thickness andcomposition, the inspecting device can conveniently be placed on thearticle, or on a calibration block machined to duplicate the idealproperties thereof, and the distance between the transducers varied toachieve maximum signal reception.

As previously indicated, the angle at which the transducers are set ischosen to correspond to the angle of refraction and angle of incidenceof the media in which the device is to be used, which for water andsteel is approximately 18° to achieve a 45° angle transmission throughthe steel. The set screws 48-48' and 50-50' enable changing the angle ofthe transducers to adjust the angles of refraction and incidence forvarying media conditions and test requirements, and openings 44 and 45are sufficiently large to permit such angular adjustment (not shown) ofthe transducers 12 and 14.

Since water is an excellent transmitter of sound, there is no need forthe use of a separate coupling medium between the transducers and theplates which are to be inspected, when the inspection is performedunderwater. If, however, the device is to be used on dry land, couplingmeans would have to be employed to conduct the beams from thetransducers to the parts to be inspected. One means of providing thenecessary coupling would be to supply water to the lower part ofopenings 44 and 46, to maintain a continuous water phase or flushbetween the face of the transducers and the article to be inspected,thus providing an uninterrupted sound path between the transducers andarticle's surface. In this regard, for use in dry environmentapplication, the carriage block 34 may conveniently be made adjustablevertically, in addition to the horizontal adjustability provided by slot22 as shown so as to permit the transducer 14 to be moved closer to thearticle's surface. Other suitable coupling means for use in a dry orland based inspection environment will be apparent to those skilled inthe art.

The support 10 may be made of any suitable material, preferably onewhich is not corroded in the environment of use, and most preferably,one which is transparent, to permit observation of the device inoperation. Suitable materials include transparent plastics such asPlexiglas or Lucite.

The transducers are selected for sensitivity penetration qualities andresolution and those illustrated herein are, for example, 5MHZ 1/2 inchdiameter transducers. A wide variety of types of transducers arecommercially available. Ultrasonic devices to which the transducers areconnected by coaxial conductors are also readily available commercially,a suitable device being a Krautkramer Model 303B, manufactured byKrautkramer-Branson Company of Bridgeport, Conn.. One such device isshown diagrammatically in FIG. 6 equipped with a cathode ray screen 58such as shown in FIGS. 2, 3 and 4.

While the particular embodiment has been described using transducer 12as the ultrasonic beam transmitter and transducer 14 as the receiver,they could also be used in reverse roles. In some circumstances, it maybe advantageous to have the two transducers switch roles intermittently,thus having the sound pass through the article first one way and thenthe other.

The technique in using the device is to push it back and forth acrossand along the weld, observing the heights of the peak No. II as the weldis traversed. A scale 64 may be provided on the front side 22 of thesupporting block 10 which is calibrated prior to the inspection andindicates for any given configuration of material the position of thesound travel through the weld relative to the interface of the edge ofthe weld and the plate. If, within this range, a loss in the height ofthe second peak is observed, it indicates an unsatisfactory conditionsuch as lack of fusion or weld penetration.

It should be understood that the present disclosure is for the purposeof illustration only and includes all modifications or improvementswhich fall within the scope of the appended claims.

I claim:
 1. An instrument for detecting defects in lap welds comprising a rigid, elongate block having a bottom planar surface and containing a recess in its front side which extends from one end to substantially the midlength of the block, said unrecessed portion of the block containing an opening from the top to the bottom, a first transducer mounted in said opening, a carriage block slidably mounted to the block in the unrecess for linear movement relative to the unrecessed portion, said carriage block containing an opening from top to bottom, a second transducer mounted in the opening in the carriage block in alignment with the first transducer, said first and second transducers being capable of generating and detecting ultrasonic beams, and means for adjusting the distance between the transducers by movement of the carriage block in the recess relative to the unrecessed portion of the block, said openings being inclined to the bottom planar surface at converging angles corresponding to the angles of incidence and refraction of the ultrasonic beams transmitted through the couplant medium with which the instrument is to be used.
 2. A device according to claim 1 wherein the transducers are mounted at angles such that the beam travels through the weld at approximately 45° to the side surfaces thereof.
 3. A device according to claim 1 wherein the couplant medium is water.
 4. A device according to claim 1 wherein the transducers are mounted at converging angles of approximately 18° from the vertical.
 5. A device according to claim 1 wherein the block has along the unrecessed portion a scale representing the position of the sound travel through the work through which the beam is to be transmitted.
 6. A device according to claim 1 wherein the recess has a tongue projecting from its face and the carriage block a groove slidingly engaged with the tongue and where there is a locking element for locking the carriage block at a predetermined select position on the block.
 7. An instrument for detecting defects in the lap welds comprising a rigid, elongate supporting block, an extension at one end of said block of lesser front-to-back thickness, the front face of the extension in conjunction with the end of the block from which the extension extends defining a recess at the front side of the block, a carriage block mounted in the recess for movement linearly relative to the end of the block from which the extension extends, said supporting block and said carriage block containing longitudinally aligned openings, inclined in converging relation to the bottom planar surface of the supporting block at angles corresponding to the angles of refraction and incidence of the medium within which the device is to be used, transducers mounted in the openings, and means for adjusting the carriage block in the recess to vary the spacing of the transducers and to fix them at a predetermined spacing.
 8. A device according to claim 7 comprising a cathode ray screen and means for displaying signals emitted and received by the transducers on the screen for comparison.
 9. An instrument according to claim 7 wherein said cathode ray screen is provided along one edge with a scale indicating the distance the signal travels and along another edge with a scale indicating the relative magnitude of the signals. 